In a vehicle powered by an internal combustion engine, an intake duct structure (intake duct structure) for the engine may be provided with a resonator for reducing noises. JP2001-207925A discloses an intake duct structure incorporated with a resonator. The intake duct structure disclosed in JP2001-207925A is formed by a first part including an upper half of a passage portion, a second part including a lower half of the passage portion and internally defining a resonator chamber, and a partition wall part interposed between the first part and the second part and defining a narrowed neck portion communicating the interior of the resonator chamber with the air passage defined in the passage portion. This intake duct structure consists of three pieces, but the partition wall part is interposed between the first part and the second part so that the three parts can be joined to one another by a single welding operation.
The intake duct structure disclosed in JP2001-207925A is advantageous in terms of the ease of manufacture, but may not be very advantageous in terms of the ease of assembling the intake duct structure to the vehicle body. In particular, when fixedly securing the intake duct structure to the vehicle body, the intake duct structure is required to be held in position by the worker while the intake duct structure is being fastened to the vehicle body. This is detrimental to the efficiency of the assembling work.